Infection of individuals by HIV results in a generalized immunosuppression that is characterized by a depletion of helper/inducer CD4+ lymphocytes. CD4+ lymphocytes recognize antigen in the context of class II MHC glycoproteins expressed on the surface of mononuclear phagocytes. The recent observation that macrophages serve as a reservoir of HIV infection raises the possibility that virus can be disseminated during antigen presentation by monocytes expressing Ia to antigen reactive, class II restricted, CD4+ lymphocytes. We propose to study the effect of HIV infection on Ia expression. We will assess not only Ia expression by monocytes from HIV infected individuals but will also infect monocytes from uninfected individuals to directly determine the effect of HIV infection on Ia expression. We will also determine the effect of AZT treatment of Ia expression. Finally, since 50% of individuals with AIDS have disseminated mycobacterial infections, we will determine the ability of monocytes from HIV infected individuals to control the growth of Mycobacterium avium.